This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Tuesday, September 20. All times are given as local St. Louis time (Central Daylight Time). For definitions of terminology used in the night sky update, click the highlighted text.
Information updated weekly or as needed.
Join us for our next star party, Friday, October 7, 2016 held in association with the St. Louis Astronomical Society. For details, see the information at the bottom of this page.
The Sun and the Moon
Sunrise is at 6:47 a.m. on Tuesday, September 20 and sunset is at 7:00 p.m. providing us with a little over 12 hours of daylight. Even after sunset, the light from the Sun will still dimly illuminate our sky for a little over 1.5 hours. This period of time is called twilight, which ends around 8:29 p.m. this week. For those with a sun dial, solar transit or local noon occurs around 12:54 p.m. this week.
Moonrise for Tuesday, September 20 occurs at 10:00 p.m. and moonset will occur at 12:13 p.m. on the following day. On Tuesday September 20 the Moon will be exhibiting a waning gibbous phase with 79% of the lunar disk illuminated. Last quarter moon occurs on September 23 at 4:56 a.m.
Fall Equinox 2016
The first day of fall this year is on Wednesday, September 22. This day is called the Autumnal or Fall Equinox. On this day the Sun will rise roughly due east and set due west giving use equal hours of day and night.
Seasons on Earth occur due to our planet’s axial tilt. The Earth is tilted about 23.5 degrees in regards to our orbital plane. As we revolve around the Sun this tilt causes the northern and southern hemispheres to be inclined towards or away from the Sun at different times of the year. This changing orientation is what causes the seasonal changes.
Ancient astronomers tracked the Sun’s position in the day sky and the other stars in the night sky to determine the time of year. From observations of astronomical phenomena such as the fall equinox cultural traditions such as agriculture were developed. An interesting place to visit regarding ancient solar astronomy is Cahokia Mounds. On Sunday, September 25 they will be holding a fall equinox sunrise observation at the Woodhenge reconstruction. This site is the reconstruction of a solar observatory that was used by the ancient Cahokians to track the Sun and other astronomical phenomena. Follow the link below for more information.
International Space Station (ISS) Observing
Visible passes of ISS from St. Louis for the week of September 20 occur in the morning and evening hours. The best of these occur on the mornings of September 21 and 23. Use the table below for information about these and other visible passes of ISS this week.
Catch ISS flying over St. Louis starting Tuesday, September 20.
Magnitude (Mag): The Measure of brightness for a celestial object. The lower the value is, the brighter the object will be.
Altitude (Alt): The angle of a celestial object measured upwards from the observer’s horizon.
Azimuth (Az): The direction of a celestial object, measured clockwise from an observer’s location with north being 0°, east being 90°, south being 180° and west being 270°.
For information about ISS flyovers and other visible satellites, visit www.heavens-above.com
Detailed information regarding all unmanned exploration of our universe, missions past, present, and planned, can be found at Jet Propulsion Laboratories:
The Planets Visible Without a Telescope
Venus can be seen low in the west about 20 minutes after sunset in the western sky. Venus sets by 8:06 p.m.
The Red planet is currently found in Scorpius rising before the Sun and can be easily seen 30 minutes after sunset in the southern sky. Mars sets by 11:09 p.m.
The ringed planet is has reached opposition and as such rises before the Sun sets. Look for Saturn alongside Mars in the southern sky about 30 minutes after sunset. Saturn will set by 10:27 p.m.
Uranus and Neptune 2016
Both of the outer gas/ice giants are once again nicely placed in our late evening skies. Neptune rises before the Sun so it is visible once the sky is dark enough about 45 minutes after sunset. Uranus follows a couple of hours later rising at 7:59 p.m. Neptune reached opposition on September 2 and will be at its brightest during the month of September. With our current weather conditions Neptune has been elusive in binoculars but for those with 42mm or larger binoculars should be able to find Neptune at its current apparent magnitude of 7.8.
Uranus is found in Pisces and will reach opposition on October 15 this year. It is already shining with an apparent magnitude of 5.7 making it an easy target in any binocular. It may grow bright enough that if in dark skies keen observers could see it naked eye.
For up to date maps of the location of Uranus and Neptune follow the link below or use the free planetarium software Stellarium.
Deep Sky Object of the Week
A few years ago the night sky update included a section that highlighted one constellation a month and a few objects of interest inside of it. Unfortunately of the 88 constellations there are only about 60 we can see in St. Louis and of these there are only so many that have enough objects to reference that would interest both beginners and advanced observers. In 2015 we changed things a bit for this section and instead of highlighting one constellation for each month we highlighted one Messier object a week using the Astronomical League’s Binocular Messier program as our guide. We will continue this into 2016 but instead of using the Astronomical League’s binocular Messier program we will use their Binocular Deep Sky Program.
The Astronomical League is an amateur astronomy society that is composed of over 240 local amateur astronomy societies across the United States and includes members at large and other supporting members. Their goal is to promote the science of astronomy through education, incentive and communication.
One of the many ways the Astronomical League has assisted amateur astronomers around the world is by creating various observing programs that highlight different aspects of astronomy and how an amateur astronomer can observe the sky and learn more about astronomy in doing so. Some of these programs are introductory and are targeted at those beginning to learn about observational astronomy and some are extremely advanced, require specialized equipment and require a large amount of time to complete. These observing programs cover most any type of object or way to observe the sky so everyone should be able to find one that matches their interests and abilities. It is important to note that these programs are not part of any class or lecture series but are rather lists of objects that highlight types of objects or observing methods relevant to astronomy. Taking part in these programs is done under one’s own choice. To officially complete each program you do have to be a member of the Astronomical League but you do not have to join to use them as observing guides or education tools. I would urge anyone interested in astronomy to look at these programs as they will help organize observing sessions and will help refine observing skills you already have. You can find out more information about the Astronomical League’s observing programs here https://www.astroleague.org/observing.html
The observing program we will use to help guide us through the 2016 observing year is the Binocular Deep Sky Program. This is a program that will appeal to both beginning and advance observers. Too often it is thought that you need to have a telescope for astronomical observations. Telescopes make great observing tools and yes they can show you more than binoculars but they do have their limitations. Cost, size, weight and complexity will often be a surprise to people when they first learn about telescopes. These factors can keep people from using telescopes they own or from buying one at all. The best advice to follow is a good observing tool is one you will use.
The binocular deep sky program is an introduction to deep sky objects beyond the Messier catalog. It will introduced viewers to the New General Catalog (NGC) and some of the lesser known deep sky catalogs such as the Stock, Collinder and Melotte. Each week we will highlight a deep sky object that is part of the Astronomical League’s binocular deep sky program. This program is tougher than Messier binocular program as the objects are not always as obvious and they will require larger binoculars than the Messier program. 50mm binoculars are recommended but many of the targets can be seen through smaller aperture instruments. I would urge each observer to fulfill the requirements of the program even if you do not intend to join the League for completion. The requirements involve logging observing data that can help refine observing skills that will be useful later down the road. If you have an interest in astronomy and learning more about observational astronomy I would also recommend checking out one of the two excellent astronomy societies near St. Louis. Both are members of the Astronomical League and both do numerous public observing nights around town. These clubs are the
If you do not live in the St. Louis, Missouri area chances are you have similar astronomical societies where you live.
The deep sky object for the week of September 6 is the open star cluster NGC 7789. Located in the constellation Cassiopeia, NGC 7789 will be seen tracking through the circumpolar sky all night long. At a distance of 6,200 light years this star cluster shines with an apparent magnitude of 6.7 making it an easy target for most binoculars. The 300 stars in this rich star cluster are estimated to be 1.6 billion years old. On Earth when these stars first started to shine it is believed a supercontinent named Columbia was still the dominant landmass of the Earth.
NGC 7789 has a Trumpler classification of II, 1, r; meaning it is well detached from background stars with little central concentration, it has very little variance in stellar magnitudes and it has a rich population with over 100 stars.
To find NGC 7789 you have to locate the W-shape of Cassiopeia. To do this simply look northeast about 10:00 p.m. and Cassiopeia will be easily seen from dark or light polluted skies.
Next identify the bright star Beta Cassiopeiae which is the western most star in the W-shape. From here grab your binocular and scan to the southwest about 2° until you find the star Rho Cassiopeiae. Once here scan about 1° south and you will find NGC 7789. It will appear as a fuzzy patch of light through most binoculars. Use the links below for help in locating NGC 7789.
As an additional treat this week I recommend doing some research on the guide star Rho Cassiopeiae. This star is a rare yellow hypergiant and is one of 12 that has been found in the Milky Way. These are rare stars because they are extremely massive and unstable. This star has the mass equivalent of roughly 30 stars. The unstable nature of stars like Rho Cassiopeiae cause them to shed off about 1/100,000 of its mass per year. This may seem like a small number but compared to the Sun that is hundreds of millions of times more than the Sun loses each year. Yellow Hypergiants are believed to be an evolutionary stage of massive stars as they evolve from their red supergiant stage into a luminous blue variable star.
Rho Cassiopeiae is about 8,200 light years away but yet it is visible to the naked eye. The reason is it is about 500,000 times more luminous than our Sun. So even at its great distance it appears quite bright. About every 50 years the star dims by about 2 magnitude because it pumps much of its gas into its expansive atmosphere. This causes the star to cool dramatically appearing as a cool M-class star. About a year after this Rho Cassiopeiae returns to its normal magnitude. The last time this happened was in 2000-2001. This is also a star that is destined to go supernova. Due to its mass loss it will likely end as a Type Ib or Type Ic supernova.
The deep sky object for the week of September 13 is the open star cluster NGC 129. Located in the constellation Cassiopeia, NGC 129 will be an observable in the northeast by 10:00 p.m. At a distance of 5,200 light years NGC 129 will shine with an apparent magnitude of 6.5. Normally this magnitude would make it an easy target but this low population star cluster is spread over 20 arc minutes of sky and will be difficult to discern as a star cluster. The 30 stars are quite young at 150 million years old. The Trumpler classification for this star cluster is IV, 2, p which means it is not well detached from background stars, it has a moderate range of stellar magnitudes and it is a poor population cluster with less than 50 stars.
To find NGC 129 you will have to locate the W-shape of the constellation Cassiopeia. Once you can find this constellation locate the stars Gamma and Beta Cassiopeiae. Once this achieved grab your binoculars and scan between the two stars. About halfway between them is where you will find NGC 129. The three brightest stars in the cluster form a bright triangle and the rest will likely appear as a dim patch of light. This will be a tough object due to its spars nature and our light pollution. Like many of the objects covered this year NGC 129 will help you hone your observing skills.
The deep sky object for the week of September 20 is the Sculptor Galaxy. Also known as NGC 253 the Sculptor Galaxy is said to be one of the brightest and easiest galaxies to see. The difficulty for us besides light pollution will be the galaxy’s southern location. NGC 253 is located in the constellation Sculptor which is visible in the south throughout the fall. NGC 253 will be at its highest altitude of 25° around 1:00 a.m.
Galaxies like star clusters have classification systems that help astronomers study these objects. The most famous of these is the Hubble Sequence. Unfortunately our target this week does not fit well into Hubble’s sequence so we will use a typology that is from the de Vaucouleurs system which is just a modification of the Hubble Sequence. In this system de Vaucouleurs complimented the Hubble Sequence by adding more complex classifications for bars, rings and arms structures present in a galaxy. Based on this scheme NGC 253 has a classification of SAB(s)c. This describes NGC 253 as a spiral galaxy with a weak bar structure and no galactic ring. It is thought SAB galaxies are an intermediary stage of a galaxy between traditional spiral and bared spiral galaxies.
At a distance of 11 million light years NGC 253 shines with an apparent magnitude of 7.6. This is also a neighboring galaxy that is part of the Sculptor group of galaxies. Another significant feature of this galaxy is it is a starburst galaxy. Starburst galaxies are galaxies that are undergoing an exceptionally high rate of star formation. This occurs primarily due to the process of galactic mergers but can also be cause by a central bar in the galaxy funneling gases into the galaxy’s center. NGC 253 is the later of these options. Due to its high rate of star formation NGC 253 is known to contain a number of super star cluster and Wolf-Rayet stars.
To find NGC 253 we will start by finding the asterism the Great Square of Autumn. By 1:00 a.m. when our target is at its highest altitude you can find the Great Square almost directly overhead. To confirm you have found the Great Square the W-shape of Cassiopeia can be found just north of the square with the Great Square itself made up of the constellations Andromeda and Pegasus. Once you have this part of the sky identified locate the two stars Alpheratz in Andromeda and Algenib in Pegasus. If you follow the direction these two stars point to the south you will find the bright star Deneb Kaitos in the constellation Cetus. Once you identify this star grab your binoculars and scan south about 10° and you will find NGC 253 in the constellation Sculptor. You can confirm your find by identifying the star Alpha Sculptoris in Sculptor. This star is about 5° below NGC 253. In binoculars NGC 253 will appear as a fuzzy lenticular patch of light. Use the maps below to help you identify all suggested guides and this week’s target. This is another week that I would highly recommend using a planetarium software such as Stellarium to help.
Our next Star Party will be held on Friday, October 7, 2016, from dusk until 10 p.m.
As part of the Saint Louis Science Center’s First Fridays, weather permitting, the St. Louis Astronomical Society and the Science Center will set up a number of telescopes outdoors and be on-hand to answer your questions. Telescope viewing begins once it is dark. Regardless of the weather on October 7, join us indoors in our planetarium theater for “The Sky Tonight”. Showtime is at 7 p.m.
This free, indoor star program will introduce you to the current night sky, the planets, and the seasonal constellations. Doors open 15 minutes before show time. Shows begins at 7 p.m. Sorry, no late admissions due to safety issues in the darkened theater.
The St. Louis Astronomical Society helps host the monthly Star Parties at the Saint Louis Science Center which are held on the first Friday of each month. Our Monthly Star Parties are open to the public and free of charge.